Can anyone recommend a suitable stronger adhesive than ordinary cement pug to re fix an exterior step which consists of a standard
450mm square slab cemented to a concrete block base? The problem seems to be the 50mm overhang presents just sufficient leverage to break the bond when a heavy footfall is on the edge.AJH
I used Gripfil Original to re-fix quarry tiles to a concrete base. It's a front path so gets heavy use. Been fine for a couple of years now
How about taking the overhang back to 30mm or 20mm by casting mortar or concrete underneath it for additional support?
What *I* would do is paint the slab and the base with a cement slurry immediate prior to using a 3:1 mix. That will get a *very* strong bond.
My old man's trick - never failed me yet for awkward jobs, like end bricks dropping off walls and things like that...
Just make a neat mix of cement-water and paint it on both surfaces then bed an new 3:1 cement sand mix when all still wet?
Thanks AJH
Add some SBR to the slurry for extra stickiness ?
Simon.
Yes.
Slurry should be like paint - gloopy.
You will get a bond more or less as strong as your substrate, possibly stronger (which is why 3:1 is not normally used for brickwork, because the bricks crack in favour of the joint).
Now we're getting serious!
I've done that when patching screed and the patch is only 10mm thick.
If the OP did that, the slab will shear its face off before the bond fails.
You can make the slurry with just SBR and cement. You can also add a small amount of SBR into the water for the mortar mix. These will give the mortar some tensile strength. Just make sure you never want to take it apart again later ;-) You can use exterior PVA instead of SBR (SBR will be better if it gets soaking wet).
I chucked some left over SBR + glass fibre reinforced screed (i.e. no stone s in it) into a plastic storage box and the result is an extremely "solid" (non-scientific term) lump of matter. In case you are wondering, I used thi s mix to bridge a gap in the underlying concrete so I wanted it as strong a s possible !
Simon.
Interesting that SBR and PVA behave quite differently in a mortar. Without constant stirring, SBR will drop out of the mix, suggesting that the liquid phase of the mortar goes its own way once it's on the surface.
Yes, you don't really notice that with SBR screed as screed is so dry - the whole lot just goes a bit gluey. Simon.
Exterior grade PVA (which is really EVA, not PVA) chemically bonds with the cement as it sets, and this is also what makes the EVA waterproof. EVA is not waterproof by itself, only when used in mortar mixes with cement.
I have less experience with SBR, and I don't think it chemically bonds with the cement so much as just glues it together, but it's waterproof by itself. PVA will behave in the same way, but is not waterproof - it slowly dissolves in water, so won't work long term in wet cement.
OK this is what I have done, painted both surfaces with a cement-SBR slurry and then made the pug with 3:1 sand:cement and SBR. We'll see how it survives.
I added some shingle to the remaining mortar and have used it to repair a pot hole on the edge between two cast in situ roadways just to see how it fairs.
AJH
Like a block of iron if my experiences are anything to go by!
Could be connected to "pugging" the material found in between joists for sound deadening ,,,
It's not my trade but is what the brickies call it in Surrey-Sussex area.
AJH
Sussex too for me... Well, East Sussex to be exact!
The term pug mill is standard in the world of clay/pottery. Nowadays often a machine that you can feed in mixed "a bit dry" and "a bit wet" clay and hopefully get a sausage of even, good consistency clay ready for use. Somewhat similar to an over-sized mincer/sausage maker.
Yup - I have a Pug Mill (pottery type) sitting under my welding bench waiting to be fixed - been there years :)
Pug is the standard term with builders round here for mortar.
Andrew
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